Coated articles are known in the art for use in window applications such as insulating glass (IG) window units, vehicle windows, and/or the like. It is known that in certain instances, it is desirable to heat treat (e.g., thermally temper, heat bend and/or heat strengthen) such coated articles for purposes of tempering, bending, or the like in certain example instances.
In certain situations, designers of coated articles often strive for a combination of high visible transmission, substantially neutral color, low emissivity (or emittance), and low sheet resistance (Rs). High visible transmission for example may permit coated articles to be more desirable in certain window applications, whereas low-emissivity (low-E) and low sheet resistance characteristics permit such coated articles to block significant amounts of IR radiation so as to reduce for example undesirable heating of vehicle or building interiors.
However, heat treatment of coated articles typically requires use of temperature(s) of at least 580 degrees C., more preferably of at least about 600 degrees C. and still more preferably of at least 620 degrees C. The use of such high temperatures (e.g., for 5–10 minutes or more) often causes coatings to break down and/or causes one or more of the aforesaid desirable characteristics to significantly deteriorate in an undesirable manner. Those in the art strive for heat treatability in certain applications, coupled with acceptable optical and solar characteristics.
Consider the following heat treatable coated article with the below-listed layer stack, where the layers are listed in order from the 6 mm thick clear glass substrate outwardly.
LayerGlass SubstrateThickness (Å)TiO233.1Si3N4110ZnO100Ag107NiCrOx36.5SnO2482.7Si3N4110ZnO100Ag159.5NiCrOx36.5SnO2100Si3N4193.4
While the aforesaid coated article is heat treatable, there is room for improvement with regard to thermal stability. For example, as shown in FIGS. 2–5, lengthy heat treatments at high temperatures tend to cause this coated article to suffer significant drops in visible transmission, significant changes in certain color value(s), and significant increases in sheet resistance (Rs). There is room for improvement in one or more of these respects.
Additionally, the aforesaid coated article is susceptible to scratching in certain instances, and is also sometimes characterized by high haze values following heat treatment.
In view of the above, it will be apparent to those skilled in the art that there exists a need for coated articles which are capable of realizing (a) improved thermal stability with regard to visible transmission, color, emissivity (or emittance), and/or sheet resistance (Rs); (b) improved mechanical durability such as scratch resistance; and/or (c) improved haze characteristics. In certain example embodiments, it may be desired that one or all of these characteristics can be achieved.